Method for machining the edges of glass elements and glass element machined according to the method

ABSTRACT

A method for the production of glass or glass ceramic elements from flat glass or glass ceramic parts is provided where the edges of the glass or glass ceramic elements are treated by a combination of two processes. The flat glass or glass ceramic element with an edge surface connecting the two side surfaces is produced. The edge surface has at least one first elongated, strip-shaped edge region and at least one second elongated strip-shaped edge region, which are formed by a ground edge. The edge regions extend in the longitudinal direction along the edge surface and along the side surfaces. The first edge region has elongated parallel filamentary damages that are parallel and adjacent to one another and, in particular, spaced apart equidistantly, in the longitudinal direction thereof extending transversely to the side surfaces and along the surface of the first edge region.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 16/104,510filed Aug. 17, 2018, which is a continuation of InternationalApplication No. PCT/EP2016/079411 filed Dec. 1, 2016, which claims thebenefit under 35 USC § 119(a) of German Application No. 10 2016 102768.5 filed Feb. 17, 2016, the entire contents of all of which areincorporated herein by reference.

BACKGROUND 1. Field of the Invention

The invention relates, in general, to the processing of the edges ofsheets of glass. In particular, the invention relates to a processing ofthe edges with different methods.

2. Description of Related Art

Typically, for the production of a flat glass or glass ceramic element,a larger flat element is divided by one or a plurality of separatingsteps and thereby brought to the desired dimension. Subsequently, ingeneral, a processing of the edge is necessary. For separation,mechanical scoring and breaking has become established practice, butalso fusing or abrasive processes such as water-jet separation areknown.

Each of these methods has certain drawbacks, such as, for instance, alow mechanical strength or a low dimensional accuracy. Thus, duringscoring and breaking, for example, the shape errors increase withincreasing thickness owing to breaks induced at an angle. In the case ofwater-jet cutting, a separating surface that runs at an angle is formeddue to the method, because, during water-jet cutting, a groove thattapers in a wedge shape is produced.

In the different separating processes, however, conchoidal fractures andmicrocracks can occur at the edges, as a result of which the resultingstrength is greatly reduced or the intended contour of the workpiece isaltered.

With increasing crack length, the strength of the edge is diminished,wherein the following applies:

$a = \left( \frac{K_{1\; c}}{2\;\sigma_{res}} \right)^{2}$

Here, K_(1c) is the critical stress intensity factor of the material, ais the crack length, and σ_(res) is the maximum stress load on the crackbefore the microcrack becomes enlarged.

Typically, during the post-processing, special geometries (C-cut, flatcut, small facets) are produced by using a special shaping tool.Depending on the input quality, this processing step is also multistageas well, with the edge being machined using different tools of differentgrit in succession.

Because the accurate course of the edge cannot always be exactlymaintained during separation, an allowance is generally reserved. Theallowance is then removed during the post-processing of the edge.

Finally, in multistage processes, it is also necessary to removesubsurface damages by a first grinding process through the steps thatfollow. Provided as the first shaping grinding step in this case iscoarse grinding for straightening the edge or for creating a (coarse)contouring of the edge, which is important, above all, in the case ofseparating methods that do not produce high dimensional accuracy. Thesecond step—fine grinding—then produces the final contour with thesurface finish corresponding to the process and accordingly with thestrength corresponding to the process. This is tedious, because finergrinding processes also remove the material more slowly, even though,this notwithstanding, a thicker layer needs to be ground away forelimination of the subsurface damages. Oftentimes, in this state, thesurface finishes do not meet the optical requirements in regard totransparency or roughness, for example. If the obtained edge quality isnot adequate, a polishing step is optionally conducted for refinement ofthe edge, said polishing step not resulting in any changes in thecontour, but solely improving the surface finish (for example, reducedroughness, higher transparency, higher strength, . . . ). All describedprocess steps can may be composed, in detail, of a plurality of separateprocess steps.

US 2015/165548 A1 describes the filamentation of a glass with subsequentpolishing of the edge that is formed. In the further process, a contouris formed through double filamentation of the edge margin regions at anoblique angle. In this case, there exists the problem that, inparticular in the case of glass that has not been prestressed, the smallperforated edge regions (with triangular cross section) have to be splitoff in a process-safe manner from bulk material and removed free ofsplinters. A similar method is also described in US 2014/239552 A1.

Accordingly, the invention is based on the object of improving the edgeprocessing for glasses and glass ceramics in terms of effort, accuracy,and production costs. The quality of the edge should thereby becomparable in terms of conchoidal fractures and microcracks to thestrength and the visual impression of at least the production methodsdescribed above.

SUMMARY

This object is achieved by the subject matter, embodiments, andenhancements presented herein.

Utilization of an ultrashort-pulse laser enables a glass to bestructured (filamented) in such a way that it can subsequently beseparated. The separation is to be assisted, if need be, mechanically orthermomechanically or in a similar manner. The edge thereby formedexhibits values comparable to ground edges in terms of strength.

Surprisingly, it has been found that, on account of the accuracies ofthe edge that can thereby be produced, subsequent process steps, such asan edge grinding, can be employed substantially more precisely. Thismeans that only one process step is needed to utilize this without anyallowance necessary due to process engineering and, accordingly, it ispossible to run the process with markedly faster process speeds. Inparticular, a coarse grinding can be dispensed with on account of thehigh accuracy during separation. Furthermore, it has also been foundthat, due to the high dimensional accuracy that is already achievedduring the separation operation, in comparison to the fine grinding inconventional multistage grinding post-processing, markedly less materialhas to be removed in the subsequent grinding. In this way, the processspeed can be increased by a factor of 2 and in fact, in general, by afactor of 2.5 or 3.

In particular, in terms of strength, the edge quality is comparable to aconventionally ground edge. Furthermore, it was surprisingly establishedthat, in terms of visual appearance, an edge produced by pre-separationusing an ultrashort-pulse laser does not noticeably differ from a groundedge. Accordingly, both processes can be combined for the final creationof an edge. It is accordingly possible to employ even geometricallysimple tools (for example, in the case of facets) and this makes theprocess chain less expensive with identical quality. The grinding volumeis thereby reduced still further, as a result of which the processingspeed is correspondingly increased and tool wear can be markedlyreduced. Furthermore, it is thereby possible to produce glass articleswith accuracies that are predetermined by the laser process and aremarkedly greater than the present-day accuracies.

In general, the invention therefore provides a flat glass or glassceramic element, the edge of which is processed by using a combinationof two methods, namely, filamentation and cleavage or separation, on theone hand, and edge grinding, on the other hand. These methods are,therefore, the insertion of filamentary damages that lie adjacent to oneanother along a line and subsequent separation along said line withformation of an edge as the first method, and processing of the edge bygrinding as the second method. In accordance with an especiallypreferred embodiment of the invention, the grinding of the edge is notproduced over the entire surface, but instead is limited to one or, inparticular, both of the strip-shaped margin regions of the edge surfacethat adjoin the side surfaces of the glass or glass ceramic element.

In particular, the invention provides for a method for the production ofglass or glass ceramic elements from flat glass or glass ceramic parts,wherein filamentary damages in the interior of the glass or glassceramic part are created adjacent to one another along a separating lineand the damages are created by laser pulses of an ultrashort-pulselaser, wherein the material of the glass or glass ceramic element is atleast partially transparent to the laser pulses, so that the laserradiation can penetrate into the glass or into the glass ceramic for thecreation of the damages in the interior, and the pulsed laser beam andthe surface of the glass or glass ceramic part are moved relative toeach other, so that the points of impingement of the laser pulses on thesurface of the glass or glass ceramic element line up next to oneanother along the separating line, and wherein after the insertion ofthe filamentary damages arranged adjacent to one another along theseparating line, the glass or glass ceramic element is released byseparation at the separating line or is worked out of the glass or glassceramic part, and wherein the edge surface of the glass or glass ceramicelement formed during separation is processed in part by grinding, sothat the edge surface has at least one strip-shaped region created bythe insertion of the filamentary damages and the separation, and oneadjoining strip-shaped region that is further processed by grinding.

These two strip-shaped regions thereby created differ, among otherthings, in terms of their surface quality, although, as a rule, thisdifference is not perceivable to the naked eye. In the edge surface thatis produced after the glass or glass ceramic element has been workedout, the previously introduced filamentary damages can be observed asstructures that extend transversely to the longitudinal direction of theedge surface and are parallel to one another. In the region that isfurther processed by grinding, in contrast, these structures areremoved, at least in part, through the removal of the material.

Accordingly, the flat glass or glass ceramic element that can beproduced by using the above-described method has two opposite-lying sidesurfaces and an edge surface that connects the two side surfaces,wherein the edge surface comprises at least one first elongate,strip-shaped edge region and at least one second elongated strip-shapededge region, which is formed by a ground edge. These edge regions extendin the longitudinal direction along the edge surface and along the sidesurface and hence parallel to the longitudinal direction of the edgesurface. The first edge region has elongated filamentary damages thatare spaced apart parallel to one another and the longitudinal directionof which extends transversely to the side surfaces and along the surfaceof the first edge region. Typically, the feed rate and also the pulserepetition rate of the laser are essentially constant during the laserprocessing. This is accompanied by the fact that the filamentary damagesare also arranged equidistant, that is with a constant center-to-centerdistance with respect to one another.

The invention is especially suited for thicker substrates. In this case,there is a special advantage that the laser penetrates into the volumeand can define there the intended cutting surface precisely through theintroduction of a damage. In contrast, mechanical methods are able toact, in general, only from the outside and this favors the “wandering”of the cutting surface and accordingly the introduction of inaccuraciesin the dimensions. In general, the invention is suited for glass orglass ceramic parts and accordingly for the production of glass or glassceramic elements with a thickness in the range of 1 to 20 millimeters,preferably in the range of 2 to 15 millimeters, especially preferred inthe range between 3 and 10 millimeters.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained below in more detail with reference tothe figures. In the figures, identical reference numbers refer torespectively identical or corresponding elements. Shown are:

FIG. 1 a laser processing device for the insertion of filamentarydamages;

FIG. 2 an optical arrangement for the generation of a Bessel beam forthe filamentation;

FIG. 3 a laser processing device for working an element out of a glassor glass ceramic part;

FIG. 4 an element worked out of a glass or glass ceramic part;

FIG. 5 the further processing of the glass or glass ceramic part bygrinding of strip-shaped edge regions;

FIG. 6 the completely processed glass or glass ceramic element;

FIG. 7 in cross section, an edge with facets;

FIG. 8 in cross section, an edge with a C-cut; and

FIG. 9 a micrograph of a filamented and subsequently ground edge.

DETAILED DESCRIPTION

For the method according to the invention, a glass or glass ceramicelement 3 with fixed dimensions is worked out of a flat glass or glassceramic part 2. FIG. 1 shows an exemplary embodiment of a laserprocessing device 1 for carrying out this step of the method. Apre-separation is carried out through insertion of elongated orfilamentary damages along a provided separating line 4. The imaginaryseparating line 4 and accordingly also the course of the inserteddamages 6 trace the outer contour of the glass or glass ceramic element3 that is to be released.

Accordingly, for the example shown in FIG. 1, a rectangular element isto be cut out of the glass part or glass ceramic part 2 corresponding tothe course of the imaginary separating line. The separating line 4 neednot necessarily run along the entire outer contour. For example, itwould also be conceivable that the outer contour of the glass or glassceramic part 2 and of the glass or glass ceramic element 3 that is to bereleased coincide in part, and no pre-separation is then to be carriedout along these regions.

In order to create filamentary damages 6 adjacent to one another alongthe separating line 4 in the interior of the glass or glass ceramic part2, an ultrashort-pulse laser 10 is provided as a component of the device1. The ultrashort-pulse laser 10 emits laser pulses 8, which impinge atthe respective point of impingement 80 on one of the side surfaces 25 ofthe glass or glass ceramic part 2 and penetrate into the volume of thepart. The laser pulses 8 are directed onto the side surface 25 in such away that the points of impingement 80 lie on the separating line 4. Bymeans of a feed device, the pulsed laser beam and the surface of theglass or glass ceramic part 2 are thereby moved relative to each other,so that the points of impingement 80 of the laser pulses 8 on thesurface 20 of the glass or glass ceramic element 2 line up adjacent toone another along the separating line. In the example shown in FIG. 1,the glass or glass ceramic element 2 is moved along the separating line4 in the direction of the arrow shown next to the point of impingement80. As a feed device in this example, an XY table 17 is provided, withwhich the glass or glass ceramic part 2 can move in the plane of theside surface 25.

The formation of an elongated filamentary damage in the material canresult, in particular, through self-focusing of the high-energy laserpulse. It is also possible to provide optics that produce an elongatefocus in the material. An example of such optics is an axicon.Preferably, the line focus has a length of 10 mm or less as well as adiameter of 10 μm or less. Regardless of the mechanism of the focusing,the damage of the glass or glass ceramic material is caused, inparticular, through the generation of a plasma by the high-energy laserlight.

The elongated filamentary damages 6 are produced by multiphotonabsorption, the activity ranges of which can be adjusted and formedthrough suitable optics. What may be involved here is a filamentationthrough self-focusing of a laser beam in consequence of the nonlinearKerr effect in the focal region of a lens, the mechanism of which isdescribed, for example, in WO 2012/006736 A2. Alternatively oradditionally, however, it is also possible by way of special optics,such as, for instance, an axicon or a lens with spherical aberration, tocreate a linear focal region, along which the multi-photon absorptionprocess can be brought about in a specific manner. Such optics aredescribed, for example, in FR 2989294 A1, KR 2014 0072448 A, or US2012/0234807 A1. The use of optics for creation of a line focus has theadvantage of not having to take into account the fragile balance betweenKerr focusing and plasma de-focusing, so that, in practice, more uniformdamages in the material can be created. It is also possible via opticsto adjust in a specific manner the intensity distribution in thematerial and accordingly also the length of the linear damages.

In general, regardless of the kind and manner of the feed, it ispreferred that the repetition rate of the ultrashort-pulse laser 10 andthe feed rate during the movement of the pulsed laser beam and thesurface of the glass or glass ceramic part 2 relative to each other isadjusted in such a way that the filamentary damages arranged adjacent toone another have a center-to-center distance in the range of 1 to 15micrometers, preferably 2 to 10 micrometers. For a faster process speed,this distance ensures that the glass or glass ceramic element 3 canstill be worked out simply and safely.

Especially advantageous for the creation of long filamentary damages is,in general, an operation of the ultrashort-pulse laser 10 in the burstmode. In this operating mode, the laser pulses 8 are not emitted as anindividual pulse, but rather in the form of pulse packets. These pulsepackets are referred to as bursts. Accordingly, in further developmentof the invention, an operation of the laser 10 is provided in the formof a successive emission of laser pulses in time in the form of burstsor pulse packets, wherein preferably each of these bursts is produced atone of the respective filamentary damages 6.

Such a pulse packet has, in general, a somewhat greater energy than anindividual pulse in the usual single-shot operation. However, the pulsesof a burst themselves contain markedly less energy than an individualpulse. Furthermore, it is typical that the pulse energies of the pulsesdecrease within a burst. For certain lasers, the energy distribution ofthe pulses within the burst can be adjusted. The burst mode cantherefore be characterized in that the laser emits pulse packets,wherein the spacing in time of the pulses within a pulse packet is lessthan the spacing in time between two pulse packets, and wherein thepulse energy of the pulses within a pulse packet drops from pulse topulse.

A suitable laser source in accordance with the present invention is aneodymium-doped yttrium aluminum garnet laser with a wavelength ofpreferably 1064±5 nanometers, but also possible are the wavelengths532±5 or 355±5 nanometers. The laser source preferably operates with arepetition rate that lies between 5 kHz and 200 kHz, preferably between10 kHz and 150 kHz, and most preferably between 30 kHz and 110 kHz. Thescanning speed can preferably be chosen such that, depending on therepetition rate, the distance between adjacent filamentary damages liesin the range of 2 micrometers to 10 micrometers.

Especially advantageous in accordance with one embodiment of theinvention is, in general, also an operating mode for which therepetition rate of the laser pulses is adjusted in the form ofindividual pulses or bursts depending on the relative speed between thelaser and the glass or glass ceramic part, in order to achieve, inparticular, a distance that also remains as constant as possible fordifferent speeds. Therefore, the adjustment is made, in particular, suchthat, at a higher feed rate, a higher repetition rate is set.

In accordance with an enhancement of this embodiment, it is therebyprovided that straight paths are traveled with higher repetition rates(and speeds) than, for example, curved path segments. In this way, it isalso possible to produce complex geometries with high accuracies, butparticularly also with high mean speeds.

In this case, the suitable pulse duration of a laser impulse lies in arange of less than 100 picoseconds, preferably at less than 20picoseconds. The pulse duration can also lie at less than 1 picosecond.The typical power of the laser source thereby lies especially favorablyin a range of 40 to 200 watts. In order to create the filamentarydamages, in accordance with an advantageous enhancement of theinvention, a pulse energy in the burst of more than 200 microjoules isused and, further advantageously, a total burst energy of more than 500microjoules.

Preferably, a laser 10 with a power in a range of about 10 to 200 wattsis used.

The laser energy deposited in the glass or glass ceramic part 3 is >300μJ, preferably >400 μJ, and most preferably >500 μJ per laser pulse, inparticular for laser pulses in the form of bursts.

In the case of an operation of the laser 10 in the burst mode, therepetition rate is the repetition rate of burst emission. The pulseduration is essentially dependent on whether a laser is being operatedin individual pulse operation or in burst mode. The pulses within aburst typically have a similar pulse length to a pulse in individualpulse operation.

The filamentary damages 6 extend, following the light propagation, fromthe surface into the material, that is, in the direction of theopposite-lying side surface. If the insertion of these damages 6 isconcluded, so that the damages form, as it were, a curtain extendingbelow the provided separating line 4, this curtain composed of filamentsthat are arranged adjacent to one another or else lie on a zone found inthe volume, then, subsequently, the glass or glass ceramic element 3that is to be produced can be worked out.

FIG. 2 shows schematically the beam path of the laser pulse 8 through anoptical element 9 for the generation of a Bessel beam. With the Besselbeam, a line focus of the length d is created, along which anessentially constant light intensity in the region of the optical axisis present. In the illustration of FIG. 2, the beam path runs from leftto right. The reference number 82 refers to the spatial intensityprofile of the laser pulse 8 prior to impingement on the opticalelement. The laser pulse 8 typically has a Gaussian intensity profile.After passing through the optical element, a spatial intensity profile84 is formed in the shape of a Bessel beam with strongly increasingintensity on the optical axis. This intensity profile is essentiallymaintained along the path d. Accordingly, the optical element 9 bringsabout a focusing on a line focus. In order to achieve a focusing of thiskind, an axicon, in particular, is suitable as an optical element 9.

In general, without limitation to the described exemplary embodiments,the separation at the separating line 4 can occur or at least can beassisted in order to work out the glass or glass ceramic element 3 alongthe separating line through local heating of the glass or glass ceramicpart (2). Especially suited for this purpose is heating by means of alaser beam. This step of the separation is illustrated by means of alaser in FIG. 3. The local heating is carried out by guiding the laserbeam 110 of a CO₂ laser, in turn, along the separating line 4 over theside surface 25 of the glass or glass ceramic part 2. The same movementmechanism as for the step of insertion of the filamentary damages offersitself for use. Accordingly, for the example shown in FIG. 3,corresponding to the arrangement of FIG. 1, the laser is likewise heldin fixed position and the glass or glass ceramic part 2 is moved bymeans of the XY table 17. This movement mechanism is obviously onlygiven by way of example. Of key importance is the relative movementbetween the point of impingement of the laser beam and the glass orglass ceramic part 2. Due to the local heating, mechanical stresses areproduced that lead to the formation of a crack 111 along the surface inwhich the filamentary damages 6 lie, and the glass or glass ceramic part3 to be worked out is separated from the surrounding material.

FIG. 4 shows the worked-out flat glass or glass ceramic part 3. Theglass or glass ceramic element 3 has two opposite-lying edge faces 25,26 as well as a peripheral edge face 24. The thickness of the element 3preferably lies in the range of 1 to 20 millimeters, more preferably inthe range of 5 to 15 millimeters. In the edge face, the laser structuresin the form of filamentary damages 6, for example, can still be seen.They extend in their longitudinal direction in the direction of the oneside surface 25 to the opposite-lying side surface 26. If theirradiation of the laser pulses 8 is perpendicular to the side surface25, then the longitudinal direction of the filamentary damagesaccordingly lies in the direction of the surface normal of the sidesurface 25.

In comparison to conventional separation methods, this method has theadvantage of a high accuracy. Thus, for a thickness of the glass orglass ceramic part of 4 mm in conventional scoring and breaking, anallowance of, for example, 0.6 mm is observed. The provided exactdimensions are then produced by grinding to the correct dimension. Aninfeed of 1-2 mm, such as, for example, 1.3 mm, per side is required forthe grinding. With increasing thickness of the glass or glass ceramicpart, the inaccuracies increase further during cutting. Accordingly, alarger allowance is to be taken into consideration.

In contrast, in the method according to the invention, at most duringclamping of the glass or glass ceramic part, inaccuracies result whenthe contour of the element to be produced cannot be traveled over in acontinuous processing step with the ultrashort-pulse laser. Suchinaccuracies are typically in the range of less than 0.2 mm, preferably0.1 mm, more preferably less than 0.05 mm.

In accordance with the invention, however, the edge processing does notconclude when the glass or glass ceramic part 3 is worked out of theglass. A mechanical fine processing still needs to be carried out.However, this mechanical fine processing is preferably carried out insuch a way that the outer dimensions are not further reduced. In anycase, the edge surface 24 of the glass or glass ceramic element 3 thatis formed by separation is partially processed by grinding in such a waythat the edge surface 24 has at least one strip-shaped region producedby the insertion of the filamentary damages and the separation, and anadjoining strip-shaped region that is further processed by grinding.

FIG. 5 shows the glass or glass ceramic element 3 in the case of thefurther edge processing explained above. The edges 27, 28 at thetransition between the edge surface 24 and the side surfaces 25, 26 arestill sharp and correspondingly sensitive. The profile of the edgesurface is altered here by edge grinding in order to make these edgesinsensitive to impacts. For this purpose, strip-shaped regions 242, 244adjoining the side surfaces 25, 26 are processed such that the edges 27,28 are rounded. In the example shown in FIG. 5, the grinding of thestrip-shaped regions 242, 244 of the edge surface 24 is carried out witha grinding device 13 that has two rotating grinding heads 14, 15. Thegrinding device 13 is moved along the marked arrow at the edge surface24, so that the areas 242, 244, including the edges 27, 28, are groundat an angle.

In general, the grinding can produce a facet, which forms a transitionfrom the edge surface 24 to the adjoining side surface 25, 26.Preferably, as is also the case for the example shown in FIG. 5, atleast one facet 20, 21 is ground at the edge of each of the sidesurfaces 25, 26.

FIG. 6 shows the completely processed glass or glass ceramic element 3with facets 242, 244 on the two sides. As a result of theabove-described production, the edge surface 24 of the glass or glassceramic element 3 then has at least one first elongate, strip-shapededge region 240 and at least one second elongated strip-shaped edgeregion—in this case, two edge regions 242, 244—which are formed by aground edge. These edge regions 240, 242, 244 extend in the longitudinaldirection along the longitudinal direction of the edge surface 24. Inthis case, the first edge region 240 has the elongated filamentarydamages 6 that are parallel and adjacent to one another andequidistantly spaced that are inserted by the laser processing. Thelongitudinal direction thereof extends transversely, preferablyperpendicularly to the side surfaces 25, 26 and along the surface of thefirst edge region 240. Because the glass or glass ceramic part 3 wasseparated at the filamentary damages 6, said damages can be present inthe surface of the first edge region 240, in particular astrough-shaped, elongated depressions.

For clarification of the previously described embodiment, FIG. 7 showsthe cross-sectional shape of an edge of a glass or glass ceramic element3 that has a faceted ground edge and has been processed as describedabove. The edge surface 24 is formed by a first edge region 240, whereinthe transition to the side surfaces 25, 26 is formed in each case by asecond edge region 242, 244 formed as a narrow facet 20, 21. Theinclination of the second edge regions 242, 244 lies in each casebetween the inclination of the first edge region 240 and the adjoiningside surface 25 or 26. The corresponding situation then also applies forthe directions of the normals. Accordingly, in this case, the secondedge regions 242, 244 each form a facet 20, 21, the normal direction ofwhich lies between the normals of the first edge region 240 and thenormals of the side surfaces 25, 26 that adjoin the facet.

FIG. 8 shows another embodiment of the invention. In this embodiment, aC-shape of the edge surface is produced by the first edge region 240 andthe second edge regions 242, 244. In accordance with this embodiment ofthe invention, in the flat glass or glass ceramic element 3, the edgesurface 24 has, in particular, at least in some areas, a C-shapedprofile, in which the first edge region 240 extends between two curvedsecond edge regions 242, 244.

As in the case of the example shown in FIG. 7, here, too, the secondedge regions 242, 244 frame the first edge region 240 and form thetransition from the first edge region 240 to the side surface 25 or 26.Owing to the linear propagation of the light, as in the case of theother embodiments of the invention, the first edge region 240 extends ina straight line in cross section. Due to the curving of the surface ofthe second edge regions 242, 244, the inclination of the surface of boththe first edge region and also the side surface approaches theinclination of these adjoining surface regions. However, it is notthereby ruled out that edges are still present at the transitions. TheC-cut is especially insensitive with respect to damages at the edge. Itis clear to the person skilled in the art that the exemplary embodimentsin accordance with FIG. 7 and FIG. 8 can also be combined with eachother. On the one hand, the peripheral edge can have sections with aC-cut and sections with facets. It is also possible at a side surface toprovide a facet in accordance with FIG. 7 and, on the opposite-lyingside, to provide a rounded edge region of a C-cut. Finally, it is alsopossible for facets to be present at both side surfaces in addition tothe rounded edge regions.

The method according to the invention will be compared below with aconventional method for the cutting of a glass or glass ceramic part 3.In both examples, a sheet of soda-lime glass with a thickness of 8 mmserved as substrate. In conventional processing, scoring was conductedwith a diamond scoring wheel and then the glass element was worked outby breaking. The insertion of the C-cut was produced in two steps, witha grit D121 and a feed of 8 m/min, then with a grit D76 and a feed of 5m/min.

In accordance with the invention, a sheet of glass was perforated bymeans of a picosecond laser with wavelength of 1064 nm, a repetitionrate of 100 kHz, and laser pulses composed of 4 bursts. The perforationdistance, that is, the center-to-center distance between adjacentfilamentary damages, was 5 μm. The separation occurred by tracing theseparating line with the laser beam of a CO₂ laser. The laser spot had adiameter of 8 mm and the laser power was 260 W. The curved edge regionsof the C-cut were inserted by a single grinding with a grit D76 and afeed of 12.5 m/min. Because the course of the edge is more exactlydefined than during scoring and breaking and only the curved transitionregions from the edge to the side surfaces need to be produced, a singlegrinding step suffices, in comparison to the conventional processingmethod. In addition, the grinding can be conducted at a higher feedrate. In general, without limitation to the special exemplaryembodiments that are shown in the figures, feed rates during grinding,that is, the relative movement between the grinding device 13 and thesurface of the glass or glass ceramic part 2, in the range of 5 metersper minute to 40 meters per minute, more preferably in the range up to20 meters per minute, are favorable for the method according to theinvention.

FIG. 9 shows a micrograph of a ground edge according to the invention,that is, a ground edge that has been pre-separated by filamentation andsubsequently ground. In this image, diagonally running grinding tracescan be seen in the region 242 and are absent in the strip-shaped edgeregion 240 produced by filamentation. However, the micrograph shows thatthe roughnesses of the two regions are similar. Optically andhaptically, the differently processed edge regions therefore appear tobe essentially indistinguishable. The filamentary damages cannot be seenin the enlargement of the images shown in FIG. 9.

LIST OF REFERENCE NUMBERS

-   1 laser processing device-   2 glass or glass ceramic part-   3 glass or glass ceramic element worked out of the glass or glass    part 2-   4 separating line-   6 filamentary damage-   8 laser pulse-   9 optical element-   10 ultrashort-pulse laser-   11 CO₂ laser-   13 grinding device-   14, 15 grinding heads-   17 XY table-   20, 21 facets-   24 edge surface-   25, 26 side surfaces-   27, 28 edge-   80 point of impingement of a laser pulse 8 on surface 20-   82 spatial intensity profile of the laser pulse 8 prior to focusing-   84 spatial intensity profile of the laser pulse after focusing-   110 laser beam of 10-   111 crack-   240 strip-shaped region processed by filamentation-   242, 244 strip-shaped region post-processed by grinding

What is claimed is:
 1. A flat glass or glass ceramic element,comprising: two opposite-lying side surfaces and an edge surfaceconnecting the two opposite-lying side surfaces, wherein the edgesurface comprises a first strip-shaped edge region and a secondstrip-shaped edge region, the first strip-shaped edge region comprisingelongated, parallel filamentary damages that are adjacent to one anotherand extend in a longitudinal direction, the longitudinal directionextending transversely to the two opposite-lying side surfaces, thesecond strip-shaped edge region being a ground edge that extends in thelongitudinal direction and joins the first strip-shaped edge region andone of the two opposite-lying side surfaces.
 2. The flat glass or glassceramic element of claim 1, wherein the second strip-shaped edge regioncomprises diagonally running grinding traces that are absent in thefirst strip-shaped edge region.
 3. The flat glass or glass ceramicelement of claim 2, wherein the grinding traces of the secondstrip-shaped edge region and the filamentary damages of the firststrip-shaped edge region have roughnesses that are similar.
 4. The flatglass or glass ceramic element of claim 2, wherein the grinding tracesof the second strip-shaped edge region and the filamentary damages ofthe first strip-shaped edge region are optically and hapticallyindistinguishable.
 5. The flat glass or glass ceramic element of claim1, wherein the edge surface further comprises another secondstrip-shaped edge region, the another second strip-shaped edge regionbeing a ground edge that extends in the longitudinal direction and joinsthe first strip-shaped edge region and the other of the twoopposite-lying side surfaces.
 6. The flat glass or glass ceramic elementof claim 1, further comprising a thickness in a range of 1 to 20millimeters.
 7. The flat glass or glass ceramic element of claim 1,wherein the second strip-shaped edge region has a C-shaped profile. 8.The flat glass or glass ceramic element of claim 1, wherein the secondstrip-shaped edge region forms a facet between the first strip-shapededge region and the one of the two opposite-lying side surfaces.
 9. Aflat glass or glass ceramic element, comprising: two opposite-lying sidesurfaces; and an edge surface having a first ground region, a secondground region, and a central region, wherein the central region has aplurality of elongated, parallel filamentary damages that are adjacentto one another and extend in a longitudinal direction, the longitudinaldirection extending transversely to the two opposite-lying side surfaceswherein the first ground region joins one of the two opposite-lying sidesurfaces to the central region, and wherein the second ground regionjoins another of the two opposite-lying side surfaces to the centralregion.
 10. The flat glass or glass ceramic element of claim 9, whereinthe first ground region and/or the second ground region lack any of theplurality of elongated, parallel filamentary damages present in thecentral region.
 11. The flat glass or glass ceramic element of claim 9,wherein the first ground region and/or the second ground regioncomprises diagonally running grinding traces that are absent in thecentral region.
 12. The flat glass or glass ceramic element of claim 11,wherein the grinding traces and the filamentary damages have roughnessesthat are similar.
 13. The flat glass or glass ceramic element of claim11, wherein the grinding traces and the filamentary damages areoptically and haptically indistinguishable.
 14. The flat glass or glassceramic element of claim 9, further comprising a thickness between thetwo opposite-lying side surfaces along the longitudinal direction in arange of 1 to 20 millimeters.
 15. The flat glass or glass ceramicelement of claim 9, wherein the first ground region and/or the secondground region comprise curved regions.
 16. The flat glass or glassceramic element of claim 9, wherein the first ground region and/or thesecond ground region comprise straight regions.